1. Field of the Invention
The present invention relates to a clutch cover assembly, and more particularly to a clutch cover assembly using a diaphragm spring and a secondary spring for urging a pressure plate into engagement with a clutch disc.
2. Description of the Related Art
In general, a clutch cover assembly is mounted on a flywheel of an engine and is used to transmit a drive torque of an engine to a transmission. Such a clutch cover assembly is mainly composed of a clutch cover fixed to the flywheel, a pressure plate for clamping a friction portion of a clutch disc into friction engagement with a surface the flywheel, and a spring member for biasing the pressure plate toward the flywheel.
In general, a diaphragm spring is used as the spring member mentioned above. The diaphragm spring is composed of a disc spring portion and a plurality of lever portions extending radially inwardly from an inner circumferential edge. Thus, the diaphragm spring has a function to bias the pressure plate and is moved to a function to release its spring force from the pressure plate. For instance, such a diaphragm spring typically has a release load characteristic D as shown in FIG. 9. As shown in the graph in FIG. 9, the force required to release engagement with the clutch disc increases at a generally constant rate as the release stroke increases. However, at a certain critical point, the force required to continue deflection of the diaphragm spring decreases gradually.
A clutch cover assembly is known in which, in order to improve the release load characteristics, a secondary conical spring is disposed between the clutch cover and an annular disc portion of the diaphragm spring. The conical spring is compressed between the annular disc portion of the diaphragm spring and the clutch cover. In this case, the biasing force of the diaphragm spring and the conical spring are combined. The force required to deflect the diaphragm spring must include force to deflect both the diaphragm spring and a load of the conical spring. At this time, for instance, the load characteristics may be adjusted by combining the portion of the conical spring where the load is large with the portion of the diaphragm spring where the release load is small, as a result of which it is possible to obtain flat release characteristics where the change of load is suppressed. It is therefore possible to enhance the operational feeling upon the release operation.
In the above-described conventional clutch cover assembly, it is necessary to center the secondary conical spring and prevent rotation of the secondary conical spring. For this reason, conventional configurations include a member such as a support ring is provided on the clutch cover side to thereby attain the retainment of the conical spring. Since the special member such as a support ring should be thus used, the number of the parts is increased.
Typically in a clutch cover assembly, the diaphragm spring is supported in the clutch cover. Generally, there are two methods for supporting the diaphragm spring, i.e., use of stud pins or support the diaphragm spring by tabs provided in the inner circumferential portion of the clutch cover.
There are clutch cover assemblies having stud pin type diaphragm spring type supports where a conical spring is employed. However, the inventors are not aware of any clutch cover assemblies in which the diaphragm spring is supported by the tabs where a conical spring is employed. Similar to that stated above, a problem with conical spring being used in a stud pin type diaphragm spring configuration is the increased number of parts necessary to support and restrain the conical spring and the diaphragm spring.